From: Bruce Momjian <bruce@momjian.us>
Message-Id: <201009201649.o8KGnAn00996@momjian.us>
Subject: Re: Binary Replication and Slony
In-Reply-To: <AANLkTin12bq-v-3j3Xg+niASj9GLbUwmJ-Eovws2o4ha@mail.gmail.com>
To: John Cheng <johnlicheng@gmail.com>
Date: Mon, 20 Sep 2010 12:49:10 -0400 (EDT)
CC: pgsql-general@postgresql.org
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John Cheng wrote:
> Congrats on the 9.0 release of PostgreSQL. One of the features I am really
> interested in is the built-in binary replication.
> 
> Our production environment has been using PostgreSQL for more than 5 years
> (since this project started). We have been using Slony-I as our replication
> mechanism. I am interested to find out the pros and cons of Slony vs the
> built-in replication in 9.0. Based on what I understand:
> 
> * Slony has a higher overhead than the binary replication in 9.0
> * When using Slony, schema change must be applied via slonik (in most cases)
> * Unfortunately, IMO it is easy to make a mistake when applying schema
> changes in Slony, fortunately, it is easy to drop and recreate the
> replication sets
> * Slony is an asynchronous replication mechanism
> * Slony allows you to replication some tables, while ignoring others
> 
> * PostgreSQL 9.0 with hot standby & streaming replication is an asynchronous
> replication mechanism
> * Overhead is low compared to Slony
> 
> Are there some cases where it is better to use Slony, for example, when you
> must specifically exclude tables from replication? I believe our system will
> be better off using the built-in replication mechanism of 9.0, and I am
> guessing most people will be in the same boat.

You have summarized the differences well.  Streaming replication has
lower overhread, but doesn't allow per-table granularity or allow
replication between different versions of Postgres.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +